Engine Trouble

[RonD]

Not quite how the system works
Vacuum leak throws off computers fuel mix calculation based on MAF(ait flow) sensor data because all the air coming into engine isn't pass thru the MAF sensor.
But O2 sensor is the final word for the computer, so computer will add more fuel until O2 sensors report good oxygen levels in exhaust, O2 sensor "sees" oxygen not fuel.

So engine wouldn't ever run Rich because of vacuum leak, exhaust leak yes.

I don't think you could have a large enough vacuum leak to cause injectors to "run out of fuel".
4.0l computer can add enough fuel to run the engine at speced RPMs, doesn't matter where the air comes from, 4 liter engine can only use XX amount of fuel at XXXX RPMs and computer has that ability.

 

[RonneyJAyala]

Not quite how the system works
Vacuum leak throws off computers fuel mix calculation based on MAF(ait flow) sensor data because all the air coming into engine isn't pass thru the MAF sensor.
But O2 sensor is the final word for the computer, so computer will add more fuel until O2 sensors report good oxygen levels in exhaust, O2 sensor "sees" oxygen not fuel.

So engine wouldn't ever run Rich because of vacuum leak, exhaust leak yes.

I don't think you could have a large enough vacuum leak to cause injectors to "run out of fuel".
4.0l computer can add enough fuel to run the engine at speced RPMs, doesn't matter where the air comes from, 4 liter engine can only use XX amount of fuel at XXXX RPMs and computer has that ability.

Well, what would cause the rev limiter type deal to occur at 3000 rpm then? I'm still going to fix my intake leak. Maybe I have an exhaust leak as well?


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[enjr44]

The rev limiter/computer keeps the engine from going over 3000 rpm in neutral.

 

[RonneyJAyala]

It's a 92 Ranger, it wouldn't have a rev limiter. Never has had one, and it does it in gear.


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[RonD]

Low fuel pressure, as said before is likely.

Computer can't add fuel that isn't there

 

[RonneyJAyala]

I had a fuel pressure test done. It was fine at 32 psi, he even floored it to where it stops at 3k and it read just fine.

Plus, if it was fuel pressure, why would it cut like a rev limiter? If it was low pressure wouldn't it hold a rpm, and not bounce around. Also, another thing is my tac signal dies when it does hit the 3k.

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[RonD]

Low fuel pressure acts like that, would start to cause engine misfiring at a certain RPM when pressure was low enough.

But if engine was misfiring during pressure test and pressure was above 25psi then that won't be the problem, it was just the most likely problem.

Does your 4.0l have a Cam Position Sensor(CPS)?
My '94 doesn't but some did, it would be at the back top of the engine, black cap with 3 wires connected.
If it does, unplug it and see if engine runs better.
CPS times fuel injectors and assists computer in spark timing advance.
When it is unplugged computer use CKP(crank position) sensor only for those functions.

Can you get a timing light?
Yes old school but still handy to have, lol.
I would hook it up to spark plug and start engine, should get a nice steady spark flash from the light.
Now raise RPMs until you get the misfiring, light will of course be flashing faster but should also be steady, if it is "misfiring" as well then I would change Coil Pack.
Test spark on 1, 2 and 3 this way, could just be one coil in the coil pack that is misfiring, each of the 3 coils in the pack spark 2 cylinders so one going bad takes 1/3 of the power away, engine would be struggling.

You can test coils with ohm meter, and you can ID a bad coil this way, but static test like this won't show a bad coil that misfires at higher RPM.

4.0l, pre-'95 uses an EDIS-6 module to spark the coil, this is usually located on the rad support, on engine bay side, or on my '94 it is on the front side of rad support.
While these hardly ever fail, it isn't never fail, so.......

 

[RonneyJAyala]

Could my truck have the CPS? I have a 92 ranger, but it has a 93 4.0 in it.
If so, you said the rear part of the motor on the top, which side?

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[RonD]

4.0l engine never had a distributor but the 2.9l engine did, and the 2.9l and 4.0l share the same block.
So the 4.0l has a distributor hole in the center top rear of the block, that is where the CPS and it's syncronizer would be.
It it doesn't have one there will be an oil pump drive under a cap covering the hole

Pictures of CPS/syncro here: http://www.therangerstation.com/tech_library/4_0-camshaft_synchronizer.shtml

 

[RonneyJAyala]

Okay, so something weird happened as I'm comming home from lunch. I decided to test the rev limiter type dealy, and instead of bouncing on 3k it went up all the way? Mind you truck has been sitting all day, and I did it as it was warming up.

Edit: Tried this morning to see if it would bounce off 3k while the truck was cold, and it did. Now I'm stumped.

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[RonneyJAyala]

So I did a compression test on my motor today, turns on passenger side cylinder bank the front two cylinders are running really low for compression (100 psi) when it's suppose to be around 150, the rest were running 135/145 psi. So I think I have a blown head gasket.


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[RonD]

Yes, that's a 30% difference.

Could be head gasket failure between the two cylinders, this wouldn't cause over heating just poor running.

You could test for that but with 100psi I would just plan on redoing the head gaskets.
Plus side is it probably isn't a crack head, as that would cause over heating, and would have higher compression numbers.

 

[RonneyJAyala]

We also did a wet compression test and it only went up to 115-120 on both cylinders.


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[cp2295]

Wouldn't necessarily cause overheating... At least when my had was cracked I noticed oil in the coolant and coolant in the oil, but she didn't overheat! Even with a deep crack between the valve seats and all over the head. These motors are stout. But yes I would replace the gasket on that side, and see what happens. Check the rocker arms and pushrods too for galling


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[RonneyJAyala]

I'm going to get a full head gasket set, plus get my heads checked out to see if they are warped. The overheating issue I believe is the thermostat, it runs off of pressure from the block. Well since there's a coolant leak inside the Pistons (tons of white smoke that reaks of gas and coolant) the engine can't build optimal pressure to open the thermostat, I know this because I don't have heat but the motor is really hot. Then the thermostat opens heat comes on, and the engine cools. I believe thisnisncausing my overheating problem. The problem where it can't go passed 3k, that may be caused by this, but I don't know.


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